Field of the Invention
The invention relates to a device for supplying fluid media that is suitable in particular even at low temperatures, that is, temperatures even below the freezing point of the fluid media. Such devices are used particularly in the context of systems for metering liquid reducing agent into exhaust systems of motor vehicles, for reducing pollutants in the exhaust gas.
Description of the Prior Art
In internal combustion engines, especially diesel internal combustion engines, in view of the more stringent exhaust gas laws expected in the next few years, the proportion of nitrogen oxides in the exhaust gas, among other components, must be reduced. For reducing the proportion of nitrogen oxide in the exhaust gas, selective catalytic reduction (SCR), for instance, is performed, in which the nitrogen oxides are reduced to nitrogen and water with the aid of reducing agents. An aqueous urea solution, for instance, is used as the reducing agent.
The reducing agent is typically stored in a tank and supplied via a line from the tank to a metering module, with which the reducing agent is injected, into the exhaust tube, for instance. One example of such a device is shown in European Patent Disclosure EP 0 982 884 A2.
Instead of the system shown in EP 0 982 884 A2, in which the reducing agent is introduced into the catalytic converter with the addition of compressed air, simpler systems are often also used, in which the liquid reducing agent is supplied from a tank (which may for instance be designed in heated form) via a supply module and corresponding lines to the metering module, so as to be injected there into the exhaust gas.
The liquid reducing agents currently usual (such as the aforementioned aqueous urea solution), however, depending on the (optionally) added antifreeze agents, freeze at between approximately −11° C. and −40° C. Thus the described system is often only indirectly available under certain ambient conditions. Special heating measures are therefore typically taken in order to convert the reducing agent in the system into the liquid state. Therefore often not only the tank but also the supply module and/or the lines used are designed as completely or partly heated. With these provisions, it is as a rule assured that the system will be operationally ready after a specified time.
Despite the aforementioned heating provisions, however, a frequent problem is that the interface between individual system components, such as the components comprising the tank, supply module and line or line segments, can be thawed only poorly because of the specified nature of the heating. Even if the individual system components themselves have thawed, in many cases the interfaces are still frozen, which reduces or even prevents the availability of the system. This is due in particular to the fact that the electric heating can be brought to the interface only with major effort and expense.
In many cases, hydraulic connection pieces are needed for the interfaces. Heating these hydraulic connection pieces, which as a rule are not part of the heating circuit or circuits of the system components, has proved to be exceedingly difficult.